(1) Field of the Invention
The present invention relates to a liquid crystal display unit having an edge light (side light) type backlight. In particular, the present invention relates to a liquid crystal display unit having good optical properties by improving light extraction efficiency and inhibiting deterioration of an optical member.
(2) Description of the Related Art
The liquid crystal display unit displays an image by controlling the optical transparency of a large number of pixels formed behind a liquid crystal panel face. The liquid crystal panel has no own light emission function and a liquid crystal display unit, generally referred to as “transmission type”, is provided with a light source called a “backlight” and the light emitted from the backlight is spread onto a rear face side of a liquid crystal panel.
The following two types of backlight are available: one type in which a large number of light sources are distributedly arranged on a rear face side of a liquid crystal panel display face, hereinafter referred to as “direct type” and another type in which a light source is attached to at least one end portion of a liquid crystal panel, hereinafter referred to as “edge light type”.
The edge light type, in which a light source is attached to an end portion of a liquid crystal panel, has an advantage in the slimness of a liquid crystal display unit over the direct type. However, the edge light type, having light sources generating much heat concentratedly arranged on the edges, tends to cause an end portion of the proximity of the light source of an optical component such as a light source or an optical guiding board to have a high temperature. Temperature rise in these portions causes degradation in optical properties due to thermal factors, such as decrease in lifetime of a light source, display uniformity of a liquid crystal panel, and thermal deterioration of an optical guiding board, which therefore need to be suppressed by a cooling structure. Additionally, the cooling structure preferably has high assemblability, and requires that the light from the light source is effectively made incident into the optical guiding board and directed toward the liquid crystal panel or that there is not such a side effect as degradation in optical properties due to any factor except heat.
As a cooling structure of the edge light type, for example, JP-A-6-51307 discloses a structure using a cold-cathode tube as a light source. This structure has such an effect that the heat from the light source of the cold-cathode tube is diffused by a thermal conduction layer provided on a rear face and a high temperature of an end portion is relieved. At the same time, a reflective layer is formed around the cold-cathode tube. Further, this structure is configured to effectively make the light from the cold-cathode tube incident into the optical guiding board while cooling.
In addition, as a light source of an edge light (side light) type backlight for applying light from right/left or top/bottom end side of a liquid crystal panel, use of a light emitting diode (LED) for the liquid crystal panel has been conventionally known.
For example, JP-A-2006-310221 discloses a structure using light sources arranged with LEDs (light-emitting diodes) in an array manner. According to this structure, a LED module in which a large number of LEDs are arranged on a slender substrate is disposed on a metal p-board bent in a 3-D manner. The metal p-board is formed by printing an insulating layer and a wiring copper foil on a metal plate and cools a light source by diffusing the heat of the light source onto the metal p-board. The portion of the metal p-board bent in a 3-D manner has a reflection board, which effectively makes the light from LED incident into an optical guiding board.
Further, for example, JP-A-2006-156324 (refer to FIGS. 39 to 41) discloses the following conventional technique of such a backlight: an optical guiding board is disposed on a rear face side of a liquid crystal panel and a LED is disposed at a side face position of the optical guiding board. Further, the above Patent Document describes a configuration in which the heat generated by LED is transferred from a light source-mounted substrate (light source fixing member) to a rear face side of a liquid crystal display unit by an L-type thermal conduction member, then transferred to a heat sink for radiation.